Apparatus for the surgical treatment of a point situated in an eye that are currently available generally have two generators each producing a beam of coherent light.
The first of these generators has a powerful laser, for example a laser having as active medium a bar of yttrium and aluminum garnet doped with neodymium (generally termed a Nd:YAG laser) which produces a beam of coherent infrared light having a wavelength of 1.06 micrometers. This laser is associated with what specialists refer to as a "Q-switch".
This Q-switch is composed of an electrooptical cell, for example a Pockels cell, arranged in the resonant cavity of the laser and able to change the factor of quality Q of this resonant cavity (hence its name "Q-switch")in such a way that all the light energy produced by the laser is concentrated in successive, very short, impulses of a few nanoseconds' duration.
When a beam of coherent light produced by a generator of this kind is focussed on a point to be treated in an eye, each impulse causes a micro-explosion which destroys the material present at that point.
The second generator of the known apparatus has a laser in the resonant cavity of which light waves can oscillate freely, that is, without a "Q-switch".
The beam of coherent light produced by this second generator is essentially designed to coagulate blood which could be discharged in the eye. The active medium of the laser of this second generator is therefore chosen so that this coherent light is well absorbed by the red pigment in the blood. An active medium of this kind is, for example, argon, in which case the coherent light emitted has a wavelength of between 488 and 514 nanometers, that is to say a colour ranging from blue to green, which can be chosen by the ophthalmologist.
Since it is absorbed by the blood which is present in all the tissues of the eye, the beam of coherent light produced by the second generator of the known apparatus only penetrates a short distance into these tissues. It cannot therefore be used when the operation to be carried out calls for the beam of coherent light to penetrate relatively deeply into the tissue of the eye.
Laboratory experiments and clinical trials have shown that operations of this type can be advantageously carried out with the aid of a beam of coherent light having a wavelength similar to that of the light emitted by lasers, the active medium of which is a bar of yttrium and aluminium garnet doped with neodymium when this beam is continuous or composed of relatively long impulses, that is when the laser producing this beam is not associated with a Q-switch.
In this context, reference is made for example to the book entitled "Neodymium : YAG Laser Microsurgery : Fundamental Principles and Clinical Applications", edited by R. M. Klapper, published by Little, Brown and Co in Boston (USA) and, more specifically, to the chapters "Microsurgery with the Neodymium : YAG Laser : An Overview" by F. Fankhauser and P. Rol, and "Neodymium : YAG Laser Capsulotomy", by T. A. Deutsch and M. F. Goldberg.
In order to perform all possible microsurgical operations, an ophthalmologist should therefore have an installation comprising, on the one hand, a known apparatus such as that described hereinabove, used to perform the classic operations, and on the other hand, a generator producing a beam of continuous or pulsed coherent light of long wavelength having an optical system adapted to this generator with which, for example, the operations described in the above book can be carried out.
An installation of this type would be cumbersome and expensive.